With the game's checkpoint system, it is possible to start any level from any stage. You can use it to skip hard stages, beat the boss flawlessly and get perfect score.

1. Think about the level you want to complete and start the other one (DO NOT start Catharsis: the game will crash).
2. Reach the stage you need.
3. Loose at this stage. And when the game restarts, return to title screen.
4. Now you can start the desired level from respective stage. You only got one try. If you fail, repeat from step one.